The present invention relates to a light emitting semiconductor device having a stripe type double hetero structure which is capable of performing oscillation in a single lateral mode.
In a double hetero structure light emitting semiconductor device, an active layer capable of performing laser oscillation is interposed between clad layers which have a larger forbidden band width and smaller refractive index than the active layer. In such a semiconductor device, the light emitted can be confined satisfactorily in a direction perpendicular to the plane of the active layer because of the presence of the clad layers. That is, the semiconductor device can operate in a single mode. However, in the lateral direction, that is, the direction parallel to the plane of the active layer, there is no structure to confine the light and therefore the operation in the lateral mode of the semiconductor device cannot be unified. In view of this, a variety of light emitting semiconductor device having different stripe structures have been proposed in the art for preventing the diffusion of light in the direction of the semiconductor junction and to thereby unify the operation in the lateral mode.
FIGS. 1 through 3 are sectional views showing examples of conventional stripe type double hetero structure light emitting semiconductor devices. In these figures, reference numeral 10 designates an n-GaAs substrate, 11 an n-GaAlAs clad layer, 12 a p- or n-type GaAs active layer, 13 a p-GaAlAs clad layer, 14 a p-GaAs ohmic contact layer, 15 a p-side electrode, 16 an n-side electrode, 17 a p.sup.++ diffusion region, 18 a p-GaAlAs layer, and 19 an oxide insulating layer.
The example illustrated in FIG. 1 is a light emitting semiconductor device of a so-called "oxide-defined stripe" type in which the p-side electrode 15 is in the form of a stripe. The device is relatively simple in structure. The distance between the active layer 12 and the p-side electrode 15 is 4 to 6 .mu.m. Unfortunately, if the width of the stripe-shaped electrode is set to less than 10 .mu.m, it is difficult to sufficiently concentrate the current in the active layer 12 and the operation in the lateral direction is liable to be unstable which is a definite drawback of the example of FIG. 1.
Shown in FIG. 2 is a so-called "diffusion stripe" type light emitting semiconductor device in which Zn, for instance, is diffused to near the junction surface of the active layer 12 and the clad layer 11 to form a high density p-type diffusion region 17. This semiconductor device is superior in its heat radiating characteristic to the device shown in FIG. 1. However, it is still disadvantageous in that it is difficult to control the depth of diffusion and its operational characteristics are lowered because of defects attributed to crystalline irregularities due to the high density impurity diffusion. Furthermore, the diffusion is effected in the lateral direction to substantially the same distance as the depth of diffusion making it difficult to form a stripe-type diffusion region 17 small in width.
The structure of the light emitting semiconductor device shown in FIG. 3 is of a buried stripe type. The manufacturing of such a device includes no diffusion step. However, the device is disadvantageous in the following points. Outside a multi-layer structure which has a stripe-shaped and which was formed by mesa-etching, the p-GaAlAs layer 18 is again grown by epitaxial growth. Thus, it is necessary to carry out epitaxial growth twice during which the interface between the active layer 12 and the p-GaAlAs layer 18 is exposed to the atmosphere. Thus, the device is liable to become defective from the interface thus exposed. In addition, it is difficult to form a multi-layer structure in the form of a stripe sufficiently small in width with mesa-etching techniques.
As is clear from the above description, conventional stripe type double hetero structure light emitting semiconductor devices have a variety of drawbacks in structure and manufacture and are often not satisfactory in performance.